But network projections said that Democrats would take control of the House for the first time in eight years, upending the balance of power in Washington where Trump enjoyed an easy ride following his shock 2016 election with Republican dominance of both chambers.

A major surge in early voting also sparked speculation that the so-called "Trump effect" was motivating progressive voters to turn out in record numbers - but as numerous election experts have pointed out, early voting has been a rising trend for years, and it's unclear whether all those early voters support Republicans or Democrats.

Results showed Democrats picking up seats in Republican-held congressional districts in Colorado, Florida, Kansas, Minnesota, New Jersey, Pennsylvania, Texas and Virginia, as voters there sent a message of repudiation against Trump.

"With Democrats' leadership in the state solidified, NY can pass policies previously blocked by Republicans to expand health care coverage, address climate change, and ensure women retain the right to make their own medical decisions", Jessica Post, executive director for the Democratic Legislative Campaign Committee, said in a statement on Tuesday.

Tuesday's elections will determine control of Congress in the final two years of Trump's term, and about 7 in 10 in voters said which party will hold control was very important as they considered their vote.

"While midterm elections are typically referenda on the president, this one is even more so because Trump is such a divisive leader and he has done everything he could to place himself at the center of key campaigns", says Jordan Tama, associate professor at American University's School of International Service. Moscow denies meddling and Trump denies any collusion.

At 11:15 pm, when Republicans had cemented their majority in the Senate but Democrats were on their way to taking power in the House, Trump tweeted that the election had been a "tremendous success".

Despite his party losing the House, Trump wrote on Twitter,"Tremendous success tonight".

History was working against the president in the Senate: 2002 was the only midterm election in the past three decades when the party holding the White House gained Senate seats.

Alongside all 435 House seats and a third of the Senate on the ballot on Tuesday were 36 gubernatorial races.

Meanwhile, Republicans Mike Braun and Kevin Cramer won Democratic-held Senate seats in IN and North Dakota, ousting incumbents Joe Donnelly and Heidi Heitkamp.

Mr Trump spent the final weeks of the campaign telling supporters that Democratic victories would threaten their safety and stability. Ted Cruz fended off Rep. Beto O'Rourke, the well-financed liberal darling, and in Tennessee, where Rep. Marsha Blackburn prevailed. They also suffered a setback in Florida, where Democrat Andrew Gillum conceded in his bid to become the state's first African-American governor. And several GOP-controlled districts where Democrats were making inroads have yet to post results. Democrat state legislator Laura Kelly will be that state's next governor. Nine GOP and 26 Democratic seats were up for election in the Senate, and 91 GOP and 22 Democrat in the House of Representatives. But, depending on the margin of victory for Democrats in the House, even that is unlikely to be immune to partisan obstruction. Among those expected were Trump's adult children, White House aides, Republican officials and presidential friends.

Millions of Americans voted Tuesday, and results have been projected in several races in the USA midterms, the critical first nationwide election seen as a referendum on Donald Trump's presidency. "They can now open investigations into the president, and we'll finally find out if Donald Trump has ever done anything unethical".

The loss of power will test Trump's political hold on House Republicans, most of whom had pledged their support for him lest they face the wrath of the party's core supporters, who remain in his corner.

Pelosi said the election Tuesday was about more than Republicans and Democrats.

With control of Congress, statehouses and the president's agenda at stake, some of the nation's top elections were too close to call.